Studies are aimed at a clearer picture of substrate binding and catalysis. Substrate binding is being studied by using as substrate amylose which has been sparsely substituted by various chemical groups, e.g. o-hydroxyethyl. Such substitutents block amylase action if they come at positions which are critical for substrate binding or catalysis, but otherwise appear in low molecular weight products (i.e., o- hydroxyethyl oligosaccharides). Structure analysis of such products will indicate how the substrate must fit onto the enzyme during catalysis. To learn more details of the catalytic mechanism, we propose to study effects of specific inhibitors. In particular, we will look for glycosyl enzyme ester intermediates by using ester-specific reagents as inhibitors. It appears well established that glycogen and amylopectin outer chains are elongated by action of conventional synthetases using nucleoside diphosphate glucoses as donors. However, amylose biosynthesis is anomalous and may involve a different mechanism. We propose testing for an insertion mechanism by using radioactive substrates and finding whether the radio-activity in amylose is located at the non-reducing end (conventional elongation) or at the reducing end (insertion).